1. Field of the Invention
This invention relates to an electrical connector, more particularly to an electrical connector for a signal transmission cable.
2. Description of the Related Art
Referring to FIGS. 1, 2 and 3, a conventional modular plug is shown to comprise a signal transmission cable 1, a dielectric housing 2 having a cable insertion end 20 and a mating end 26 that is opposed to the cable insertion end 20, and a plurality of conductive terminals 22. The signal transmission cable 1 is a local area network (LAN) cable and has four twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) that are enclosed by an insulative covering 10. Each of the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) has a conductive wire 101 that is surrounded by an insulative layer 100. The twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) include a first twin-twisted strand (d1, d2) for transmitting signals, a second twin-twisted strand (b1, b2) for network telephone use, a third twin-twisted strand (a1, a2) for receiving signals, and a fourth twin-twisted strand (c1, c2) for modem use and other purposes. In assembly, the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) are untwisted and straightened and are then are inserted into a cable receiving space 21 through the cable insertion end 20 of the dielectric housing 2. The ends of the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) extend to a plurality of terminal grooves 23 formed adjacent to the mating end 26. The terminals 22 are inserted into the cable receiving space 21 through the terminal grooves 23 and pierce the insulative layers 100 for electrical connection with the conductive wires 101, respectively.
If the signal transmission cable 1 is a local area network cable of category 4, the frequency thereof can only reach 40 MHz. Therefore, such a signal transmission cable 1 can only be used in 10 Base T (IEEE 802.3 telecommunication standard). The arrangement of the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) in the dielectric housing 2 for such a signal transmission cable 1 is shown in FIG. 4. To meet the requirements for high network communication speed and high quality, a high-speed local area network cable is developed to reach a higher frequency, i.e. 100 MHz. Therefore, the high-speed local area network cable can be used in 10 Base T and 100 Base T. In this case, the arrangement of the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) in the dielectric housing 2 is shown in FIG. 5.
The aforementioned conventional modular plug suffers from the following disadvantages:
1. Insertion of the untwisted and straightened twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) into the dielectric housing 2 through a narrow insert hole formed in the cable insertion end 20 is difficult to perform during assembly of the conventional electrical connector.
2. Untwisting and straightening the twin-twisted strands (d1, d2, b1, b2, a1, a2, c1, c2) will reduce the frequency to which the single transmission cable can be used and will produce crosstalk, thereby affecting adversely the network telecommunication speed and quality.
3. In either case of the local area network cables of category 4 or category 5, the first twin-twisted strands (d1, d2) and the second twin-twisted strands (b1, b2) are twisted relative to one another. Therefore, when signals are transmitted from the first twin-twisted strand (d1, d2), it is liable to be interfered by the second twin-twisted strand (b1, b2), thereby resulting in noise. This will adversely affect the network telecommunication speed and quality. The noise interference is particularly serious when the signal transmission speed of the signal transmission cable is increased to about 300 MHz.